A selective catalytic reduction (SCR) system may be used in an exhaust treatment or aftertreatment system to remove or reduce nitrous oxide (NOx or NO) emissions coming from the exhaust of an engine. SCR systems often include an injector for spraying a reductant, such as urea, into the exhaust flow.
The injector is typically positioned to spray the reductant toward a center of the exhaust flow, so that the reductant is sufficiently mixed with the exhaust flow and does not impact the walls of the exhaust piping. In certain exhaust pipe configurations, it may be advantageous to locate the injector within the exhaust pipe envelope in order to direct the reductant along the desired path. U.S. Patent Application Publication No. 2011/0079003 to Sun et al., for example, discloses an indentation mount for a reductant injector that can be used with a curved exhaust pipe. An indentation is provided that projects into the exhaust pipe. The indentation includes a wall capable of supporting the injector at an orientation that will produce a reductant flow stream in the desired direction.
While the indentation disclosed by Sun et al. allows the injector to be located in a desirable position inside the exhaust pipe envelope, the injector is more directly subjected to the high temperatures of the exhaust flow. Mounting the tip flush with the indent plate, as shown in Sun et al., may boil the reductant and form deposits in the tip that restrict reductant flow. In addition, the higher heat environment inside the exhaust pipe envelope may adversely affect components of the injector made from materials rated for lower temperatures. Recessing the tip away from the exhaust flow, as shown in U.S. Pat. No. 7,971,428 to Kimura et al., may mitigate exposure of the injector to higher temperatures, but may also introduce a recirculation flow that directs droplets of reductant back toward the tip which again may form deposits that block the injector nozzle.